Remake PostComments rendering
Remake PostComments rendering

(Tested for regressions: still plays nice with archive revival position
and omitted comments.)

This FIXES the issue when the FIRST expanded comment gets collapsed back
after loading omitted comments.

This also FIXES that super annoying issue with editing the LAST comment,
when any new realtime comment ruins your changes in the textarea.

Both fixes come from the fact that now comments never[1] change their
groups in DOM: the first comment will always stay in {firstComment},
the last one will always stay in {lastComments}.

[1] Well, at least not on the events of loading omitted comments and
new realtime comments. It still possible they would change groups when
a comment is deleted, but that happens much less often.

clbn/freefeed-gamma,clbn/freefeed-gamma,clbn/freefeed-gamma